1. Field of the Invention
The present invention relates to a hand held telephone set and an audio processing method suitably applied to a hand held telephone set having a music playback function capable of listening to a stereo music by a both-ear mount type earphone.
2. Description of the Related Art
In recent years, there has been frequently used a hand held telephone set comprising multiple functions such as an information search function or a hand free function as well as a telephone function. For example, a single-ear mount type earphone microphone is connected to the hand held telephone set so that a user can communicate with a counterpart by using this earphone without holding the telephone set main body.
FIG. 1 is an imaginary view showing an exemplary configuration of a hand held telephone set 10 with an earphone microphone according to prior art. In the hand held telephone set 10 shown in FIG. 1, a liquid crystal display 23 is mounted upwardly on its full face so as to display a counterpart telephone number, a message, or various contents of information and the like. An earphone terminal (jack) 20 is mounted to a right side of a mount position of the liquid crystal display 23 so as to mount a plug 97 provided at one end of an earphone cable 96.
A normal single-ear mount type earphone 94 is provided at the other end of this earphone cable 96, and a microphone 95 is provided at an intermediate position of a cable that reaches this earphone 94. Occasionally, these earphone 94 and microphone 95 are generally referred to as an earphone/microphone. The earphone 94 is used as a telephone receiver during response to a phone call so as to output a monophonic audio. The microphone 95 acquires the ambient sound or is used as a speaker during response to a phone call. A small sized speaker 24 for a telephone receiver is mounted upwardly of the liquid crystal display 23. When an earphone is not mounted, the counterpart audio is output during response to a phone call.
In addition, an antenna 26 is mounted to the upper left of the telephone set main body, and electric waves are transmitted to and received from a radio base station (not shown). A key array 27 for controlling this liquid crystal display 23 to be displayed is mounted to the telephone set main body. This key array 27 consists of numeric keys 0 to 9 and symbol keys # and * so as to be operated by a user.
A small sized microphone 28 for a speaker is mounted downwardly of the key array 27. When an earphone is not mounted, the user's audio is detected during response to a phone call. An operation button 25 is mounted between the liquid crystal display 23 and the key array 27 so as to input operation information during user operation. For example, a volume is increased or decreased by so called volume controlling the operation button 25.
FIG. 2 is a block diagram depicting an exemplary internal configuration of an audio processing unit 1 with a side sound superposition function in a hand held telephone set 10. The audio processing unit 1 shown in FIG. 2 has an amplifier 7 capable of being volume controlled by the operation button 25. In the hand held telephone set 10, audio information DIN/DOUT transmitted/received through a radio base station is a monophonic audio with a low frequency bandwidth (300 Hz to 3,400 Hz).
Namely, digital audio information DOUT decoded by a receiving signal processing unit 5 is output to a digital/analog (D/A) converter 6 through a mixer 9. In the D/A converter 6, after the digital audio information DOUT has been converted into an analog audio signal SOUT, the converted signal is converted into a proper audio level with an amplifier 7. Then, an analog audio signal (hereinafter, referred to as a downward audio signal) SOUT is output to an earphone 94 through a coupling capacitor C.
On the other hand, the microphone 95 is connected to the amplifier 2 through an earphone terminal 20. Then, an audio signal (hereinafter, referred to as an upward audio signal) including the ambient sound SIN is amplified, and then, is output to an analog/digital (A/D) converter 3. In the A/D converter 3, an analog audio signal SIN is converted into digital audio information DIN, and then, is output to a transmission signal processing unit 4.
When a connection point between the A/D converter 3 and the transmission signal processing unit 4 is defined as “p”, a side sound amplifier 8 is connected between the connection point “p” and the mixer 9, and then, the upward audio information DOUT including the ambient sound is amplified so as to be delivered to the mixer 9. In the mixer 9, part of the audio information SIN including the ambient sound is combined with the downward audio information DOUT. In the side sound amplifier 8, a gain is fixed by a side sound control signal S1′ from a control device 51 so as to fix the signal level of the ambient sound (hereinafter, referred to as a side sound level). This is because the type of earphone connected to the earphone terminal 20 is directed to a single-ear mount type earphone 94, and the ambient sound can be easily recognized by the other ear (hereinafter, referred to as an ambient sound superposition function).
In the meantime, recently, highly value added products such as hand held telephone set 10 having an audio playback function incorporated therein are popular, and in particular, there is a growing need to use a both-ear mount type, i.e., stereo type earphone/microphone. In such type of highly value added product, it is preferable that, when one utilizes a telephone function, one can play back a monophonic audio; and when one utilizes a music playback function, one can play back a stereo audio.
However, during use of the hand held telephone set 10, as compared with a time when a single-ear mount type earphone/microphone handling a monophonic audio is mounted, when a both-ear mount type earphone/microphone handling a stereo or monophonic audio is mounted, ear holes of both ears are covered with the earphone, whereby the user's sensitivity of the ambient sound is lowered.
Therefore, with respect to the both-ear mount type earphone/microphone, when an ambient sound superposition function for the both-ear mount type earphone/microphone is applied as is, the sensitivity of the ambient sound is lowered as compared with the single-ear mount type. Thus, there is a problem that safety is degraded. In particular, in the case where an attempt is made to apply a stereo headphone almost covering the entirety of both ears to the hand held telephone set 10, this problem arises significantly.